In an electric machine rotor provided with a plural number of magnetic poles, arranged substantially at equal intervals along the circumference of the rotor, each magnetic pole has a direct pole axis, or a direct axis. Two adjacent direct pole axes form an angle that is bisected by a quadrature axis. The reactance corresponding to the direct pole axis is called a direct-axis reactance and the reactance corresponding to the quadrature axis a quadrature-axis reactance. A reluctance torque is proportional to difference of inverse values of the quadrature-axis reactance and the direct-axis reactance, which difference can be written as 1/Xq−1/Xd. Therefore a reluctance torque can be increased by increasing the direct-axis reactance or by reducing the quadrature-axis reactance.
A known rotor of a reluctance machine includes a rotor core having a plurality of flux guide sections located along circumferential direction of the rotor core, each of the plurality of flux guide sections including a plurality of flux paths made of a material of high permeance and a plurality of flux barriers made of a material of low permeance. The flux paths and flux barriers are located alternately along radial direction of the flux guide section. For mechanical reasons there are bridges made of a material of high permeance connecting adjacent flux paths.
The bridges cause leak flux from one flux path to another. The leak flux decreases efficiency and maximum torque and increases no-load current thereby deteriorating electrical properties of the electric machine. Therefore minimizing leak flux in bridges improves electrical properties of the electric machine.